23,583 research outputs found
Bayesian nonparametric models for peak identification in MALDI-TOF mass spectroscopy
We present a novel nonparametric Bayesian approach based on L\'{e}vy Adaptive
Regression Kernels (LARK) to model spectral data arising from MALDI-TOF (Matrix
Assisted Laser Desorption Ionization Time-of-Flight) mass spectrometry. This
model-based approach provides identification and quantification of proteins
through model parameters that are directly interpretable as the number of
proteins, mass and abundance of proteins and peak resolution, while having the
ability to adapt to unknown smoothness as in wavelet based methods. Informative
prior distributions on resolution are key to distinguishing true peaks from
background noise and resolving broad peaks into individual peaks for multiple
protein species. Posterior distributions are obtained using a reversible jump
Markov chain Monte Carlo algorithm and provide inference about the number of
peaks (proteins), their masses and abundance. We show through simulation
studies that the procedure has desirable true-positive and false-discovery
rates. Finally, we illustrate the method on five example spectra: a blank
spectrum, a spectrum with only the matrix of a low-molecular-weight substance
used to embed target proteins, a spectrum with known proteins, and a single
spectrum and average of ten spectra from an individual lung cancer patient.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS450 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A Neural Network for Synthesizing the Pitch of an Acoustic Source
This article describes a neural network model capable of generating a spatial representation of the pitch of an acoustic source. Pitch is one of several auditory percepts used by humans to separate multiple sound sources in the environment from each other. The model provides a neural instantiation of a type of "harmonic sieve". It is capable of quantitatively simulating a large body of psychoacoustical data, including new data on octave shift perception.Air Force Office of Scientific Research (90-0128, 90-0175); Defense Advanced Research Projects Agency (90-0083); National Science Foundation (IRI 90-24877); American Society for Engineering Educatio
Detecting Extrasolar Planets with Integral Field Spectroscopy
Observations of extrasolar planets using Integral Field Spectroscopy (IFS),
if coupled with an extreme Adaptive Optics system and analyzed with a
Simultaneous Differential Imaging technique (SDI), are a powerful tool to
detect and characterize extrasolar planets directly; they enhance the signal of
the planet and, at the same time, reduces the impact of stellar light and
consequently important noise sources like speckles. In order to verify the
efficiency of such a technique, we developed a simulation code able to test the
capabilities of this IFS-SDI technique for different kinds of planets and
telescopes, modelling the atmospheric and instrumental noise sources. The first
results obtained by the simulations show that many significant extrasolar
planet detections are indeed possible using the present 8m-class telescopes
within a few hours of exposure time. The procedure adopted to simulate IFS
observations is presented here in detail, explaining in particular how we
obtain estimates of the speckle noise, Adaptive Optics corrections, specific
instrumental features, and how we test the efficiency of the SDI technique to
increase the signal-to-noise ratio of the planet detection. The most important
results achieved by simulations of various objects, from 1 M_J to brown dwarfs
of 30 M_J, for observations with an 8 meter telescope, are then presented and
discussed.Comment: 60 pages, 37 figures, accepted in PASP, 4 Tables adde
Nanoparticle-doped electrospun fiber random lasers with spatially extended light modes
Complex assemblies of light-emitting polymer nanofibers with molecular
materials exhibiting optical gain can lead to important advance to amorphous
photonics and to random laser science and devices. In disordered mats of
nanofibers, multiple scattering and waveguiding might interplay to determine
localization or spreading of optical modes as well as correlation effects. Here
we study electrospun fibers embedding a lasing fluorene-carbazole-fluorene
molecule and doped with titania nanoparticles, which exhibit random lasing with
sub-nm spectral width and threshold of about 9 mJ cm^-2 for the absorbed
excitation fluence. We focus on the spatial and spectral behavior of optical
modes in the disordered and non-woven networks, finding evidence for the
presence of modes with very large spatial extent, up to the 100
micrometer-scale. These findings suggest emission coupling into integrated
nanofiber transmission channels as effective mechanism for enhancing spectral
selectivity in random lasers and correlations of light modes in the complex and
disordered material.Comment: 22 pages, 6 figure
Understanding hydrogen recombination line observations with ALMA and EVLA
Hydrogen recombination lines are one of the major diagnostics of H II region
physical properties and kinematics. In the near future, the Expanded Very Large
Array (EVLA) and the Atacama Large Millimeter Array (ALMA) will allow observers
to study recombination lines in the radio and sub-mm regime in unprecedented
detail. In this paper, we study the properties of recombination lines, in
particular at ALMA wavelengths. We find that such lines will lie in almost
every wideband ALMA setup and that the line emission will be equally detectable
in all bands. Furthermore, we present our implementation of hydrogen
recombination lines in the adaptive-mesh radiative transfer code RADMC-3D. We
particularly emphasize the importance of non-LTE (local thermodynamical
equilibrium) modeling since non-LTE effects can drastically affect the line
shapes and produce asymmetric line profiles from radially symmetric H II
regions. We demonstrate how these non-LTE effects can be used as a probe of
systematic motions (infall & outflow) in the gas. We use RADMC-3D to produce
synthetic observations of model H II regions and study the necessary conditions
for observing such asymmetric line profiles with ALMA and EVLA.Comment: MNRAS in pres
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